1. Field of the Invention
The present invention relates to a braking apparatus, including a catch brake and an overspeed prevention device, for a rail-bound carriage of an inclined or vertical elevator.
2. Description of the Related Art
Conventional rail-bound inclined and vertical elevators are provided with catch brakes, in accordance with international standards, in order to bring the carriage or cage to a standstill during emergencies, such as when a cable breaks or the carriage or cage exceeds a maximum allowable travel speed. Primarily, friction brakes having friction linings which engage the rails are used as the catch brakes.
However, in these arrangements, the stopping distance between the grasping of the catching device and the ultimate stopping of the carriage cannot be clearly determined in advance, because it is a function of the instantaneous coefficient of friction at the rails. For example, the rails are made in general of structural steel having untreated surfaces and can become partially corroded or covered with ice, thus affecting the frictional coefficient. Elevators erected outside, in particular, suffer greatly from these problems.
Such inclined elevators also are used in buildings, for example, to transport freight. Blocking devices such as catch brakes and/or overspeed safety devices are also provided for these elevators. These blocking devices forcibly lock the rails, or alternatively, lock into the rail guide according to, for example, DE-GM 77 27 207, which describes a blocking and catching device with a spring prestressed eccentric as the cam disk which clamps the carriage against a braking block at the rail. Such blocking devices effect virtually no predictable stopping distance. Moreover, when they grasp the rail, this grasping is associated with corresponding long braking decelerations and undesired noise.
Another example of a conventional catch brake and overspeed safety for a rail-bound vertical elevator is described in DE-PS 119 240. In the apparatus described in that document, two rotatable eccentric disks, which are connected together by a shaft, are provided as the catching device. The eccentric disks act without sliding friction on the appropriate rail, and they press against a brake block to insure engagement. The axis of rotation of each eccentric disk is disposed at right angles to the direction of motion of the cage, and is braced via a spring or an hydraulic buffer against the cage frame.
In this conventional catch brake, the lift at the eccentric disk corresponds directly to the damping distance, which is at a right angle to the lift. The eccentric disk does not act on the rail, but rather, during the braking operation, rides on the rail. Therefore, the damping distance is quite short, so that the braking deceleration is correspondingly high as soon as the catching device grasps. Further, the slope of the curve of the eccentric disk must be small, so that its engagement with the rail remains within the range of self-locking friction.
Also, in such an arrangement, the damping distance can be less than the complete revolution of the eccentric disk. In addition, for this known arrangement, a spring is also suitable for damping the kinetic energy of the cage.